1. Field of the Invention
The present invention relates to an information processing system which can check a secondary storage medium having a prescribed relation with the information processing system and a secondary storage device therefor. More specifically, the invention relates to an information processing system such as a video game machine, a personal computer or the like which can prevent illegitimate reproduction of a secondary storage medium such as an optical disk used for the image processing system.
2. Description of the Prior Art
In an information processing system such as a video game machine using a secondary storage medium such as an optical disk storing a game program or the like, it is desirable to prevent illegitimate reproduction of information stored on a secondary storage medium. It is also desirable that the authenticity of a secondary storage medium be ensured.
Further, if a secondary storage medium such as an optical disk (a CD-ROM) is used for a video game machine or the like, the storage capacity of CD-ROM is very large and a game can be played for a long time. A user may then need to save backup data at the end of each play in a cartridge for the CD-ROM. In such a case, if a CD-ROM for a different game is inserted in the console of the video game machine when the same game is intended to be started again, the backup data for a different game are written erroneously in the disk cartridge. Therefore, there is a need to prevent such inconsistency of the CD-ROM and the backup data.
U.S. Pat. No. 4,799,635 and Japanese Patent laid open Publication 2-31256/1990 (first and second prior art) of the present applicant disclose techniques for preventing illegitimate reproduction of a program stored in a secondary storage medium. In the technique described in the first prior art, a master semiconductor element is installed in an image processor such as a video game machine, while a slave semiconductor element having a prescribed relation with the master is installed in an external storage device such as a ROM cartridge attached to the video game machine. The master semiconductor element exchanges data with the slave, and when the exchanged data have a predetermined relationship, the central processing unit included in the image processor is activated. Thus, the authenticity is decided by confirming that an external storage device does not include a slave semiconductor element which generates data having a prescribed relation with the master generated data. If it is decided that an external storage device does not include a slave semiconductor element which has the prescribed relation, the external storage device cannot be used.
As to an external storage device wherein a secondary storage medium can be inserted in or removed from a case, the above-mentioned first prior art has a problem that the authenticity of a secondary storage medium cannot be surely decided if a secondary storage medium reproduced illegitimately is contained in a case with a true slave semiconductor element.
In the second prior art reference, a part of the data in a program memory to be read for an inherent object of the program is stored in a monitor ROM in order to prevent reading data from the program memory when not used for the inherent object. If the program memory is used normally, the data sent to the address and data buses are compared with the data stored in the monitor ROM. If the comparison does not result in a match, a memory bank change is not enabled.
In the above-mentioned second prior art, the legitimacy cannot be surely decided if the data read from a program memory for an inherent use includes a conditional branch. Further, the second prior art cannot be applied to a secondary storage medium such as an optical disk which is not a semiconductor memory because the address and data buses cannot be monitored for media other than semiconductor memories.